The object may be null even after being enclosed in an if statement

In my Vue component, I have implemented the following method:

dataURLtoBlob(dataurl: string): Blob {
    const arr: string[] = dataurl.split(",");
    if (arr) {
        if (arr[0]) {
            const mime = arr[0].match(/:(.*?);/)[1];
            const bstr = atob(arr[1]);
            let n = bstr.length;
            const u8arr = new Uint8Array(n);
            while (n--) {
                u8arr[n] = bstr.charCodeAt(n);
            }
            return new Blob([u8arr], { type: mime });
        }
    }

    return new Blob();
},

Despite including if statements to handle potential issues, I am encountering a TypeScript error:

81:34 Object is possibly 'null'.
    79 |             if (arr) {
    80 |                 if (arr[0]) {
  > 81 |                     const mime = arr[0].match(/:(.*?);/)[1];
       |                                  ^
    82 |                     const bstr = atob(arr[1]);
    83 |                     let n = bstr.length;
    84 |                     const u8arr = new Uint8Array(n);

What am I missing here?

Here is the content of my tsconfig.json file:

{
  "compilerOptions": {
    "target": "esnext",
    "module": "esnext",
    "strict": true,
    "strictNullChecks": true,
    "jsx": "preserve",
    "importHelpers": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "sourceMap": true,
    "baseUrl": ".",
    "types": [
      "webpack-env",
      "mocha",
      "chai"
    ],
    "paths": {
      "@/*": [
        "src/*"
      ]
    },
    "lib": [
      "esnext",
      "dom",
      "dom.iterable",
      "scripthost"
    ]
  },
  "include": [
    "src/**/*.ts",
    "src/**/*.tsx",
    "src/**/*.vue",
    "tests/**/*.ts",
    "tests/**/*.tsx"
  ],
  "exclude": [
    "node_modules"
  ]
}

Answer №1

The indication here is not about the possibility of arr[0] being null; rather, it pertains to the potential null result from the .match(/:(.*?);/) operation. To handle this scenario, you can use the following check:

const match = arr[0].match(/:(.*?);/);
if (match) {  
  const mime = match[1];
  // ... additional code here
}

Answer №2

Make the adjustment from arr[0].match(/:(.*?);/)[1]; to arr[0].match(/:(.*?);/)?[1];

The source is the second index, not the first.

Answer №3

Here is an alternative way to rewrite it:

function convertDataURLtoBlob(dataURL) {
    const dataArray = dataURL.split(',');

    if (!Array.isArray(dataArray) || !dataArray[0] || !dataArray[1])
        return new Blob();

    let mimeType = dataArray[0].match(/:(.*?);/)[1];

    if (!mimeType)
        return new Blob();

    const binaryString = atob(dataArray[1]);
    let length = binaryString.length;
    const uint8Array = new Uint8Array(length);

    while (length--) {
        uint8Array[length] = binaryString.charCodeAt(length);
    }

    return new Blob([uint8Array], { type: mimeType });  
}

This approach avoids deep nesting of code blocks, making it easier to read and understand.

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